what rope are you using? cotton might be easier to begin with although jute once cleaned and softened is for some people a bit easier for ties,and what width? 6-8 mm is best probably 6 to start with.
only do 2-3 wraps to begin with. make sure the rope doesnt twist or move while you are working, the best way of judging tightness is to ensure once tied you can comfortably put 2 fingers between your skin and the rope.
a bit like judging shoe sizes lol and keep things simple.

its always a safe bet to learn a little about your body, where tendons,muscles nerves etc are situated.

try this link...
http://www.ds-arts.com/RopeArt/tutorials.html

its also be a good idea to check out links for self bondage vids and tutorials,though good ones can be a bit harder to find.